As an example of a conventional image reading apparatus, there is known a flatbed scanner which can read both a reflection original and transparent original (see, e.g., Japanese Patent Laid-Open No. 2001-313784). FIG. 9 shows an example of such flatbed scanner.
To read a reflection (paper) original set on an original table glass 2, an optical unit 3 which is arranged inside the original table glass 2 and can read an original line by line is linearly moved in the scanning direction using a guide member such as a guide shaft 4 or the like.
The optical unit 3 is attached to a timing belt 6 engaged with a driving motor 5. The optical unit 3 moves in the scanning direction upon rotation of the driving motor 5.
As shown in FIG. 4, an image of an original is guided to a lens 8 by a plurality of mirrors 7a, 7b, 7c, and 7d inside the optical unit 3. The lens 8 forms the image of the original on a photoelectric conversion element 9 such as a CCD or the like. The formed image of the original is converted into electrical signals by the photoelectric conversion element 9.
In the flatbed scanner shown in FIG. 9, an illumination unit 14 for reading a transparent original is incorporated in an original platen 13. FIG. 5 is a sectional view showing an example of the arrangement of the illumination unit 14. The illumination unit 14 is fixed on the back of the original platen 13 and comprises an illumination lamp 15, reflecting sheet 16, light guide member 17, light diffusion sheet 18, inverter circuit (not shown), and the like. The illumination unit 14 has a known arrangement as a sidelight-type surface light source device. A light beam emitted from the illumination lamp 15 is finally diffused by the light diffusion sheet 18 on the light-emitting surface of the light guide member 17 and exits downward, thereby forming planar illumination light.
To read a transparent original (negative or positive film), an original platen white background 11 for reflection original reading which is so attached as to cover the illumination unit 14 is first removed, and a transparent original 10 is set below the illumination unit 14. Sheet-like light is applied by the illumination unit 14 from above the transparent original, and the light having passed through the original is photoelectrically converted by the optical unit 3 inside the platen glass 2.
As described above, the user needs to remove the original platen white background 11 every time he/she wants to read the transparent original 10 such as a film or the like by a conventional image reading apparatus. This is very troublesome.
To ease a problem in attachment/detachment, in some cases, holes 11a to be hooked are formed in the original platen white background 11, and projections 12 corresponding to the holes 11a to be hooked are formed at the back of the original platen 13, as shown in FIG. 9. With this arrangement, by engaging the projections 12 in the holes 11a to be hooked, the original platen white background 11 (to be also referred to as the white background 11 hereinafter) can be attached/detached relatively easily. However, if attachment/detachment of the original platen white background 11 is repeated, the holes 11a to be hooked may break.
There is also proposed a method of providing a base resin member having a thickness of about 2 mm as the backing of the white background 11 and fitting the resin member into a fitting unit for attachment on the back of the platen (see, e.g., Japanese Patent Laid-Open No. 2003-75944). However, this method requires an additional cost of providing the base. Also, the method increases the size of the platen, thus increasing the size of the entire apparatus.
If the white background 11 is detachable, and the detached white background 11 is carelessly placed on, e.g., a dirty desk, the white background 11 becomes dirty. If the user inadvertently places the white background 11 on a sharp-pointed projection, the surface of the white background 11 may be damaged or may be broken at worst.